1. Field of the Invention
The present invention relates to a keyboard musical instrument.
2. Description of the Related Art
Conventionally, there have been electronic pianos having a simple action mechanism which uses springs or weights in order to bring the key touch of the electronic pianos close to that of an acoustic piano. Furthermore, there have been known arts for realizing the key touch of an acoustic piano not by providing the simple action mechanism but by sensing a velocity and a force of a depression of a key to exert an external force on the key from under the key by use of an actuator (e.g., Japanese Patent Publication No. 3772491, Japanese Examined Patent Publication No. 07-111631 and Japanese Patent Publication No. 3191327).
In acoustic pianos, the thickness of strings varies according to pitch, while the size and the mass of hammers also vary according to pitch. In general, bass keys have hammers having heavier mass to strike thicker strings, resulting in heavier touch of the keys. On the other hand, the touch of treble keys is lighter. When a case where a key is played fortissimo is compared with a case where the key is played pianissimo, the case where the key is played fortissimo provides a player with heavier touch of the key.